Histology of Neuron Principle cells of Nervous Tissue Consist of 3 parts : CELL BODY (perikaryon/soma) A single AXON Multiple DENDRITES07/12/2012 3
CELL BODY (PERIKARYON)• Central portion of the cell• Generally are polygonal• Different shape and size characteristic regions of nervous system• Contain : Nucleus and Perinuclear cytoplasm Nucleus :• large, spherical to ovoid and centraly located• a single prominent nucleolus• finely dispersed chromatin Cytoplasm : contains :• R.E.R and S.E.R.• Polyribosomes• Basic dyes (a+b) Nissl Bodies• Golgi complex 07/12/2012 4
• Multiple elongated processes• Cytoplasmic~perikaryon (devoid golgi complex)• Receiving stimuli•Single process up to 100 cm•Originate from axon hillock•Devoid ribosome•conducting impulse away from the soma•It maintains Axonal transport
NEURONS CLASSIFICATION :According to the size and shape of the processes07/12/2012 7
NEUROGLIAL CELLS• Metabolic and mechanical support for neuron• Have phagocytic function• 10 times abundant than neurons• Neuroglial cells undergo mitosis• CNS neuroglia Includes the following cell types : 1. Oligodendrocytes 2. Astrocytes 3. Ependymal Cells 4. Microglia PNS neuroglia following cell types : 1- Schwann Cells 2- Setellite Cells 07/12/2012 8
CNS neuroglia Includes the following cell types :1- Oligodendrocytes – Produce myelin sheath (electrical insulation) in CNS – A single cell wrap several axons (40 to 50) – Form nodes of Ranvier2- Astrocytes – Pedicles binds to capillaries and to the pia mater form glial limitans – Controlling the ionic & chemical environment of neurons – Energy metabolism – Form cellular scar tissue – Form the blood-brain barrier
3- Ependymal Cells • Low columnar ciliated epithelial cells line the ventricles of the brain & central canal spinal cord • Formation of choroid flexus produce CSF • Facilitates the movement of CSF 4- Microglia • Scattered throughout the CNS • Clearing debris • Act as APC • Protect the CNS from viruses and microorganism
PNS neuroglia Includes the following cell types :1- Schwann cells• surround all axons of neurons in the PNS creating a neurilemma around them.Neurilemma allows for potential regeneration of damaged axons• creates myelin sheath around most axons of PNS2 - Satellite cells• support groups of cell bodies of neurons within ganglia of the PNS
•Grey matter consists ofneuronal cell bodies neuropil (dendrites and unmyelinated axons) glial cells (astroglia and oligodendrocytes)•Grey matter contains neural cell bodies, in contrast to white matter,which does not and mostly contains myelinated axon tracts.•The color difference arises mainly from the whiteness of myelin•White matter is composed of bundles of myelinated nerve cell processes.•consists mostly of glial cells and myelinated axons that transmit signals from one region ofthe cerebrum to another and between the cerebrum and lower brain centers.•Its white color is due to its usual preservation in formaldehyde.
NERVE FIBERS– Consist of axons enveloped by a special sheath– Group of fibers constitute the peripheral nerve– Two types :1- Myelinated fibers A single Schwann cell wraps around single axon form myelin sheath nodes of Ranvier2 - Unmyelinated fibers A single Schwann cell envelopes several axon Fibers enveloped within simple clefts of Schwann cells
CONNECTIVE TISSUE INVESTMENTS OF NERVES • Epineureum – Dense collagenous Con. Tissue with thick elastic fiber – Prevent damage by overstreching • Perineureum – Dense con. Tissue – Layers of epithelioids – Isolates neural environment (blood-nerve barrier) • Endoneureum – Loose con. Tissue – Regulation of microenvironment of nerve fiber 1607/12/2012
GANGLIA• Ovoid structure containing neuronal cell bodies, glial cells supported by connective tissue• Function : Relay stations to transmit impulses• Types : 1- Sensory Ganglia (cell bodies of sensory neuron) • Unipolar cell bodies enveloped by cuboidal capsule cells – Cranial ganglia : Associated with the cranial nerve – Spinal ganglia : Associated with the spinal nerve 2 -Autonomic Ganglia (cell bodies of postganglionic autonomic nerves) • Multipolar neuron enveloped by satellite cells • Some are located within certain organ (intramural) 07/12/2012 17
MENINGES • The dura mater – dense, collagenous connective tissue • The arachnoid layer: – fibroblasts, collagen & elastic fibers – Layer in contact with dura mater & a system of trabeculae – Form arachnoid villi • The pia mater – Loose con. Tissue with blood vessel – There is a physical barrier between pia mater & neuron07/12/2012 19
Cerebellar Cortex •Surface of cerebellum show transverse fissures which divide the cerebellum into a number of lobules .•Section of cerebellar cortex shows three layers, from out to inside are:1 - Molecular Layer. :• Outer most layer mainly consists of cell processes.•These cell process may be dendrites or unmyelinated axon.•In this layer make the profuse synapses2 - Purkinje Cell layer :•This layer contains the cell bodies of large multipolar neurons called Purkinje cells.•The purkinje cell consists large flask shaped body.•cytoplasm contains large number of Nissl granules.3- Granular Layer :•This layer consists of thickly populated small cells called granule cells.•This layer shows irregular scattered lighter staining area called as glomeruli or island.